1. Field of the Invention
The present invention relates to a conductive wiring comprising silver or silver alloy and to a display panel substrate using the same.
2. Description of the Related Art
There are required the higher density of mounting electronic components or integrated circuits onto a printed circuit substrate, a display panel substrate used for a flat panel display device or the like, and also the narrower lines of wiring are required for the substrates. Thus, it is demanded that a wiring material should have a low resistivity.
As a use of a display panel substrate, there is an organic electroluminescence display panel for example.
The organic electroluminescence display panel has a plurality of organic electroluminescence devices formed on the substrate in a predetermined pattern. Each organic electroluminescence device comprises one or more thin films of organic compound materials at least one of which exhibits the electroluminescence (hereinafter also referred to as “EL”) which is emits light in response to a current injected thereinto.
Generally, the organic EL device includes a transparent electrode as an anode, at least one organic compound thin film and a metal electrode as a cathode, which are laminated on a transparent substrate in due order. The organic compound thin film (so-called “organic functional layer”) maybe a single light emitting layer, or a laminate which includes a three-layer structure composed of an organic hole transport layer, a light emitting layer and an organic electron transport layer, or a two-layer structure composed of an organic hole transport layer and a light emitting layer. The organic EL device may also include an electron or hole injection layer inserted between appropriate ones of these layers.
When the predetermined pattern is a grid matrix, for example, such a matrix type EL display panel has an image display array comprised of a plurality of light emitting pixels of organic EL devices arranged at respective intersections of intersecting rows and columns. The matrix display type one is composed of row electrodes including transparent electrode layers, organic functional layers, and column electrodes including metal electrode layers which intersect the row electrodes. These layers are laminated in sequence. The row electrodes are each formed in a strip shape, and arranged in parallel with each other with a predetermined spacing therebetween. The same is applied as well to the column electrodes. In this way, the display panel of matrix type has a display array region comprised of light emitting pixels which are formed of a plurality of organic EL devices positioned at respective intersections of a plurality of row electrodes with a plurality of column electrodes.
Since the organic EL device is of an electric current injection type, its consumption of electric power greatly depends on the resistivity of the electrode line. Thus, a low resistive material is strongly required for the row and column electrodes of the organic EL device otherwise a serious voltage drop occurs as involving in the luminance in homogeneousness to ruin the display quality.
There is a problem that the transparent electrode materials used for the anode such as indium tin oxide (ITO) or the like have high sheet resistance values, although a low resistive material is required for the wiring line connecting the electrodes to each other in the display array region of the substrate.
To lower the resistance of wiring, there is an attempt to use a metal line having a low resistivity as an auxiliary electrode for the wiring line connecting the transparent electrodes (the anodes) to each other in the display array region. Namely, the conventional manufacturing process of the EL display panel involves the steps of patterning the ITO anodes on the substrate, patterning the auxiliary metal lines, patterning the organic functional layers, patterning the ramparts, patterning the cathodes and connecting the cathodes and anodes to the corresponding external terminals.
Generally, the narrower the wiring line is formed to improve the luminance of each pixel in the organic EL display panel, the greater the numerical aperture becomes. Thus, an indispensable condition of the electrode material is to have a low resistivity.
Aluminum (Al) based materials is generally known as a low resistivity wiring material. When using the Al-based materials for a thin-film, the resistivity of the thin-film is limited at approximately 4 μΩ·cm at most. In addition, when using the Al-based materials for the wiring lines on the organic EL display panel, it is a problem that the Al-based materials shows an electrochemical reaction with ITO generally used for the transparent electrode.